This invention relates to hot isostatic presses which are used for the treating of articles or items by heat and pressure. Particularly, this invention is directed to an improved hot isostatic press apparatus whereby there is a more even cooling of the plurality of items which are treated at once enabling a more rapid resolution of the cooling cycle operation whereof each and every item can be cooled to the same temperature within the same time period.
Hot isostatic presses are used to treat or produce various metallic, ceramic and similar items by subjecting the items to relatively high pressure while they are in a hot and plastic state. Castings often include small internal voids or shrinking defects.
Apparatus for conducting such heat treatment processes generally include a pressure vessel which contains cooling coils or a cooling jacket on the outside thereof and insulation on the inner walls. Electrical resistance and other heat eminating structure are generally used to heat a treatment chamber within the pressure vessel.
Typically, a compressor located externally to the pressure chamber is utilized to feed an inert gas under high pressure into the pressure vessel and thereby the treatment chamber. Gas pressures can range from 1000 to 30,000 p.s.i. and above, while temperatures developed by the heating elements can range from 500 to 2000.degree. C.
Greene, U.S. Pat. No. 3,168,607, teaches a method and apparatus for heat treating articles. Greene discloses a cylindrical or oblong pressure vessel having a distinct elongate treatment area within and separate heat supply and cooling supply chambers. A positive pressure or, alternately, a partial vacuum is developed by an apparatus external to the pressure vessel, while a impeller type circulating fan situated at one end of the Greene vessel circulates either heating air or cooling air, depending upon the position of a plate valve, into the heat treatment area from one end.
Isaksson, U.S. Pat. No. 4,131,419, like Greene, discloses a cylindrically-shaped pressure treatment vessel. Here gases may be circulated from the heated inner space past and outer walls and through conduits 19,21 by operation of a valve 20 and in another embodiment by operation of valve 20 and pump 26. Isaksson has his cooled gases enter only at the bottom of his inner treatment space at its periphery and exit at the top at its periphery.
Smith, et al, U.S. Pat. No. 4,235,592, like Greene and Isaksson, discloses a cylindrically-shaped pressure treatment vessel. Smith, et al. cause a forced circulation of either hot gases, FIG. 3, or cooled gases, FIG. 4, similar to Greene. Smith, et al., however, utilize a slide plate diverter type valve, to increase the path of the gas flow past the cooled walls. Gas circulation enters the bottom of the treatment chamber and exits at the top, only.
Bowles, U.S. Pat. No. 4,217,087 teaches an isostatic apparatus for the treatment of articles with great heat and great pressure. Bowles teaches an oblong shaped or cylindrical-shaped pressure vessel having a cylindrically shaped heat treatment area within. Pressures are developed by an external structure to the pressure vessel and by expansion upon heating. A pressure operated valve at one end of the cylindrical treatment chamber is opened to allow a circulation of the heated inert gas past the outer cold vessel through natural convection. This Bowles pressure vessel is positioned in an upright manner with the cylindrical heat treating area standing upright, the cooler gas tending to travel downwardly past the cold vessel wall and to enter the heat treatment area through the open valve to fill the void left by the rising hot gas within and forcing the hotter gas out of the top of the cylindrical treatment area.
An object of the present invention is to provide a pressurized heat treating structure for articles, the structure having an inert gas circulating apparatus selectively operated for circulating the pressurized gas through the treatment area for cooling.
A second object of this invention is to provide such a heat treatment structure with more even flow of the cooling inert gas during a cooling portion of the treatment cycle.
A further object of this invention is to provide the heat treatment structure with a double walled chamber, establishing a passageway for the flow of the inert gas, and an inlet from the pressure producing structure and incorporating a diffusing function for a more even flow of cooling circulation over each and every one of the articles held within.